1. Field of the Invention
The present invention relates to an IR-ray absorptive compound and an optical recording medium utilizing the same. In particular, the present invention pertains to an IR-ray absorptive compound which provides an optical recording medium with improved durability in repeated reproduction and light resistance.
2. Related Background Art
Generally, optical recording media such as, for example, optical discs or optical cards record information at high density using optically detectable small pits (of approximately 1 .mu.m) on a thin recording layer provided on a substrate having a spiral, circular or linear groove thereon. By scanning a laser beam converged on the surface of the recording layer, the recording layer absorbs laser energy to form the optically detectable pits.
According to a heat mode recording system, the recording layer absorbs heat energy and forms a small concave portion (the pit) through evaporation or melting at that site. By using an organic dye thin film to provide a recording layer with high reflectance, the optical contrast of the recording pit can be set at a high level. For example, when polymethine, azulene, cyanine or pyrylium type dyes, etc. having high light absorption relative to laser beam are used for the organic dye thin film, a light absorptive reflective film exhibiting metallic luster (i.e., a reflectance of 10 to 50%) can be obtained, whereby an optical recording medium capable of laser recording and reflective reading can be obtained. Additionally, when a semiconductor laser with an oscillation wave length of 600 to 800 nm is used as the laser light source, there is the particular advantage that the device can be made smaller in size and with lower cost. However, organic dye thin films had the problems that recording and reproduction characteristics and storage stability may be lowered, because they generally deteriorate upon the application of heat and light, etc.
To cope with such problems, U.S. Pat. No. 4,656,121 has proposed a method to improve light resistance by incorporating an aminium salt or diimonium salt of a triarylamine type compound incorporated in a polymethine type dye.